The Nervous System

Functions

• Reception• Interpretation• Integration• Control of homeostasis• Mental Acuity• Control of Muscle and Glands

Anatomic Divisions of the Nervous System

The Central Nervous System Brain and Spinal Cord

The Peripheral Nervous System Nerves and Ganglia

Physiologic Divisions of the Peripheral Nervous System 1. Sensory- (Afferent) carries messages to the CNS

2. Motor- (Efferent) Somatic- Carries messages away from the CNS,

from the brain to the skeletal muscle. This is voluntary action

Autonomic –Controls cardiac muscle, smooth muscle and glands and is under involuntary control

Enteric- associated with digestive tract

The Nervous System Cell• The neuron Consists of a cell body,

dendrites and axons They receive the stimuli and

transmit the action potential

The Electrical Impulse

Resting Membrane PotentialAction PotentialThe SynapseReflexes

The Nervous System Tissue

• Neuron• Neuroglia- support cells• Myelin Sheaths – axon is either

myelinated or unmyelinated• White matter and Gray Matter- Gray- cortex and nuclei in the brain

and ganglia of PNS White_ nerve tracts in CNS and

nerves in PNS

The Neuralgia

The Brain Divisions

Cerebrum Diencephalon Cerebellum Brainstem

The Brain Division

• Cerebrum- Consists of Two Hemispheres Hemispheres are Subdivided

into Lobes Frontal Parietal Occipital Temporal

The Hemispheres of the cerebrum • Each hemisphere controls the

opposite half of the body• Commissures connect the two

hemispheres• The left hemisphere dominates in

analytical skills , the right dominates for spatial perception and musical ability

Divisions of the Brain

• Diencephalon Thalmus- main sensory

relay center Epithalmus- pineal gland Hypothalamus- maintains homeostasis

Brain divisions

• Cerebellum- in back attached to the brainstem

Cerebellum

• The Cerebellum is involved in balance and muscle coordination.

• An important function of the cerebellum is to compare the intended action with what is occurring and modify it

• If damage to the cerebellum, there is a decrease in muscle tone and, balance

Division of Brain Brainstem- Ascending and descending tracts

Divisions: Medulla Oblongata- heart rate , breathing, swallowing and

balance

Pons- relay nuclei between cerebrum and cerebellum

Midbrain- involved in visual and hearing reflexes

Reticular formation- maintains consciousness and sleep wake cycles

BRAINSTEM

The Twelve Cranial Nerves

I Olfactory II Optic III Oculomotor IV Trochlear V Trigeminal VI Abducens VII Facial VIII Vestibulocohlear IX Glossopharyngeal X Vagus XI Accessory XII Hypoglossal

The Cranial Nerves – nerves coming right off the brain

• There are twelve Cranial Nerves• 3 are sensory• 4 are motor• 1 both motor and sensory• 1 somatic motor and

parasympathetic• 3 with all three functions• 4 are parasympathetic

The Meninges or Coverings

• The Central Nervous System is covered by three protective layers:

• Dura Matter• Arachnoid Matter• Pia Matter

The Ventricles

• In the brain and spinal cord there are fluid filled cavities :

• lateral ventricle • third ventricle • cerebral aqueduct • fourth ventricle• central canal

The Cerebrospinal Fluid

• The Cerebrospinal Fluid is formed in the ventricles

• How does it circulate?• It is made by the choroid plexus then

exists through the fourth ventricle and it reenters the blood through the arachnoid granulations in the superior sagital sinus

The Spinal Cord

• Extends from the foramen magnum to the second lumbar vertebrae after which it is called the cauda equina

• Central part is Gray matter and the Peripheral part is White Matter forming the nerve tracts

• Roots of the Spinal Nerves Extend out of the cord

Spinal Nerves: 31 pairs of Spinal Nerves• Exit from the cervical, thoracic, and sacral regions

The nerves are grouped into Plexuses Cervical Plexus- contains Phrenic Nerve Brachial Plexus- nerves to upper limb Lumbosacral Plexus- nerves to the lower limb

How do we sense

Ascending Tracts transmit the action potential from

the periphery to the brain each tract contains a specific type

of sensory information• Project to the primary area of the

cerebral cortex

Ascending Tracts

• Spinothalmic- pain temp, light touch tickle itch

• Dorsal Column proprioception, deep pressure and vibration

• Spinocerebellar- proprioception to the cerebellum

How do we respond

Descending Tracts• Upper motor neurons in the cerebral

cortex connect to the lower motor neurons in the spinal cord, brainstem and cerebellum and send out a specific motor response

Descending Tracts for movement Table 8.5

• Direct lateral corticospinal anterior corticospinal Indirect Rubrospinal reticulospinal vestibulospinal

Ascending Descending

Simple Reflex

Autonomic Nervous System

• Divided into Sympathetic N.S. Parasympathetic N.S. Enteric N.S.

Sympathetic N.S.

• Prepares person for action by increasing heart rate, blood pressure and respiration rate. “The Fight or Flight Response”

• Associated with the thoracic and lumbar nerves ( T1- L2)

Parasympathetic N.S.

• Involved in vegetative activities such as digestion of food, defecation and urination. Slows heart rate and respiration

• Located in cranialnervesIII,VII,IX, X and sacral nerves S2-S4

Enteric N.S.

• Associated with the digestive tract

Neurotransmitters

• Acetylcholine-

• Norepinephrine-